1. Field of the Invention
This invention relates to a wireless transmission system (including also a wireless communication device implemented in one housing), a wireless communication device for the reception side and a wireless communication method. More particularly, the present invention relates to a mechanism wherein space division multiplexing is applied to wirelessly transmit a plurality of transmission subject signals.
2. Description of the Related Art
As a technique for implementing a high-speed signal transmission between different electronic apparatus disposed in a comparatively short range (for example, within several centimeters to ten and several centimeters), or within an electronic apparatus, for example, a LVDS (Low Voltage Differential Signaling) is known. However, together with further increase of the amount of transmission information and further increase of the speed of transmission recently, increase of power consumption, increase of an influence of signal distortion by reflection and so forth, increase of unnecessary radiation and so forth have become problems. For example, the LVDS reaches a limit where a signal such as a video signal (including an image pickup signal), a computer image or the like is transmitted at a high speed (on the real time basis) in an apparatus.
As a countermeasure against the problem of increase of the speed of transmission data, it seems a possible idea to increase the number of wiring lines to decrease the transmission speed per one signal line by parallel transmission of signals. However, the countermeasure just described gives rise to increase of the number of input and output terminals. As a result, complication of a printed board or a cable wiring scheme, increase of the size of a semiconductor chip and so forth are required. Further, since a large amount of data is transmitted at a high speed along a wiring system, a problem of electromagnetic field interference occurs.
All of the problems involved in the LVDS or the technique of increasing the number of wiring lines are caused by transmission of a signal through an electric wiring line. Therefore, as a method for solving a problem caused by transmission of a signal along an electric wiring line, it seems a possible idea to eliminate electric wiring lines for signal transmission.
Also it seems a possible idea to apply space division multiplexing where a plurality of communication units are provided on the transmission side and the reception side to carry out duplex transmission. However, where the space division multiplexing is applied, an interference countermeasure between channels is required. It is a possible idea to apply a MIMO (Multi-Input Multi-Output) system as a technique for solving the problem described above (refer to, for example, Japanese Patent Laid-Open No. 2009-055228, Japanese Patent Laid-Open No. 2009-049632 and Japanese Patent Laid-Open No. 2009-33588, hereinafter referred as Patent Documents 1 to 3, respectively).
Patent Documents 1 to 3 are directed to wireless transmission in a comparatively long range with respect to wireless transmission within an apparatus or between different apparatus and disclose application of a MIMO process in combination with an OFDM modulation method. In other words, the MIMO process disclosed in Patent Documents 1 to 3 depends upon the OFDM modulation method.